A pre-drive amplifier, a drive amplifier, and a main amplifier of a High Power Amplifier (HPA) in Long Time Evolution (LTE) communication and WiMax-FDD system receive and amplify a gate bias, and the gate bias is always applied regardless of time to continuously operation the HPA. Accordingly, the HPA continuously amplifies a signal in a transmission Tx mode, the amplified signal passes through a Band-Pass Filter (BPF) and then transmitted to an antenna Ant. This is why a frequency band of a transmission Tx mode and a frequency band of a receiving Rx mode differ from each other in a general FDD communication system.
However, the frequency band of a transmission Tx mode and the frequency band of a receiving Rx mode differ from each other in a TDD system such as WiMax and TD-LTE systems. Because the frequency band of a transmission Tx mode and the frequency band of a receiving Rx mode are the same in communication using a TDD mode, if an HPA always operates in a TDD communication system, great Tx leakage noise occurs. Accordingly, in a receiving Rx mode, this reduces a receiving Signal-to-Noise Ratio (SNR). For this reason, a switch of relatively high capacity is used at an output terminal of the HPA. However, since an RF communication switch S/W of high capacity has a very high cost and limitation in capacity, a simple RF S/W of high capacity is used.
A high output amplifier operates in a Tx mode using Gate bias on/off technology of an HPA but an operation of the high output amplifier is restricted in a Rx mode in a currently used TDD system. Owing to use of such modes, a Tx leakage noise level may be reduced less than −100 dBm and does not influence a receiving SNR characteristic degradation in a Rx mode to stably perform mobile system communication.
It is difficult to use an HPA for an FDD system in the TDD system. Conversely, an HPA for the TDD system may not be used in the FDD system. However, both of the HPA for an FDD system and the HPA for the TDD system are used in a recent system such as a recently developed LTE system and WiMax system in which the FDD and TDD systems coexist. Presently, the FDD system and the TDD system have been independently developed to increase a developing cost and human power twice. Moreover, due to a request of a business owner, if a system simultaneously using the two modes is needed, the two types of HPA should be provided and used, respectively.
In this case, price competitiveness and a space side of a system are very poor. First of all, rapid response to the request of the business owner is now required. To meet the requirements, because a new product should be again made in an existing mode, there is a need for much time and effort.